The invention relates generally to techniques for monitoring the condition of a drive train, and more specifically to a technique for monitoring the condition of gears and bearings within a gearbox of a drive train.
A gear is a machine part that is designed to mesh with another similar machine part to transmit rotational motion. The most commonly used gears include planetary gears, spur gears, helical gears, bevel gears, worm gears, and rack and pinion gears. Gears mesh with each other in many different ways to transfer motion from one gear to another. In addition, gears can be used to increase or decrease the speed of rotation. For example, a smaller gear driven by a larger gear will have a greater speed of rotation than the larger gear. Conversely, a larger gear driven by a smaller gear will have a lower speed of rotation than the smaller gear. Gears may be housed in a gearbox. Gearboxes are used to transmit rotational motion in many different types of systems. A gearbox typically consists of at least one gear set and bearings to enable the gears to rotate.
The gears and bearings in a gearbox may have defects, or they may fail over time, or they may simply wear out. For example, the loads and stresses that are imposed on the bearings and gears may exceed acceptable limits, leading to failure or damage to the gears or bearings. The damaged or failed components may be replaced once their existence is known. Alternatively, the teeth may simply begin to wear down through prolonged usage.
Vibration analysis is an established non-intrusive technique for monitoring the condition of mechanical components within rotating machines. For example, the condition of a component may be determined by considering the frequency and magnitude of vibration signals produced by the component. Generally, components in good condition, e.g., gears with complete sets of teeth, produce smaller amplitude vibrations than components in poor condition, e.g., gears with chipped or missing teeth. The frequencies of the vibrations produced by the gears are unique to the gear design and shaft rotation speed. One conventional technique of vibration analysis involves measuring a critical frequency of a vibration-generating component and measuring the amplitude of the vibration signal at more than one harmonic frequency of the critical frequency, then comparing the amplitudes to the amplitudes of vibration signals at adjacent harmonic frequencies. However this method may not be practical because the resonance frequency is variable.
Accordingly, there is a need for a technique for accurately detecting and identifying gear-meshing faults and bearing faults in a gearbox.